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Instrumental-Variables Simultaneous Equations Model of Physical Activity and Body Mass Index: The Coronary Artery Risk Development in Young Adults (CARDIA) Study
University of Massachusetts Medical School Faculty Publications
  • Katie A. Meyer, University of North Carolina at Chapel Hill
  • David K. Guilkey, University of North Carolina at Chapel Hill
  • Hsiao-Chuen Tien, University of North Carolina at Chapel Hill
  • Catarina I. Kiefe, University of Massachusetts Medical School
  • Barry M. Popkin, University of North Carolina at Chapel Hill
  • Penny Gordon-Larsen, University of North Carolina at Chapel Hill
UMMS Affiliation
Department of Quantitative Health Sciences
Date
9-15-2016
Document Type
Article
Abstract
We used full-system-estimation instrumental-variables simultaneous equations modeling (IV-SEM) to examine physical activity relative to body mass index (BMI; weight (kg)/height (m)(2)) using 25 years of data (1985/1986 to 2010/2011) from the Coronary Artery Risk Development in Young Adults (CARDIA) Study (n = 5,115; ages 18-30 years at enrollment). Neighborhood environment and sociodemographic instruments were used to characterize physical activity, fast-food consumption, smoking, alcohol consumption, marriage, and childbearing (women) and to predict BMI using semiparametric full-information maximum likelihood estimation to control for unobserved time-invariant and time-varying residual confounding and differential measurement error through model-derived discrete random effects. Comparing robust-variance ordinary least squares, random-effects regression, fixed-effects regression, single-equation-estimation IV-SEM, and full-system-estimation IV-SEM, estimates from random- and fixed-effects models and the full-system-estimation IV-SEM were unexpectedly similar, despite the lack of control for residual confounding with the random-effects estimator. Ordinary least squares tended to overstate the significance of health behaviors in BMI, while results from single-equation-estimation IV-SEM were notably different, revealing the impact of weak instruments in standard instrumental-variable methods. Our robust findings for fixed effects (which does not require instruments but has a high cost in lost degrees of freedom) and full-system-estimation IV-SEM (vs. standard IV-SEM) demonstrate potential for a full-system-estimation IV-SEM method even with weak instruments.
Rights and Permissions
Citation: Am J Epidemiol. 2016 Sep 15;184(6):465-76. Epub 2016 Sep 9. Link to article on publisher's site
Related Resources
Link to Article in PubMed
Keywords
  • body mass index,
  • endogeneity,
  • epidemiologic methods,
  • fixed effects,
  • health behaviors,
  • instrumental variables,
  • semiparametric methods,
  • simultaneous equations
PubMed ID
27614300
Citation Information
Katie A. Meyer, David K. Guilkey, Hsiao-Chuen Tien, Catarina I. Kiefe, et al.. "Instrumental-Variables Simultaneous Equations Model of Physical Activity and Body Mass Index: The Coronary Artery Risk Development in Young Adults (CARDIA) Study" Vol. 184 Iss. 6 (2016) ISSN: 0002-9262 (Linking)
Available at: http://works.bepress.com/catarina_kiefe/263/